Projectile for limited range training ammunition

ABSTRACT

A ball or projectile for small caliber ammunition is disclosed. The  projele is useful in training ammunition for the training of personnel on firing ranges having a limited area and a maximum range which is below the range of the standard service round for the weapon on which the training is conducted. The projectile has a body including an ogival forward section, a cylindrical center section, and a conical trailing section. A plurality of fins is mounted longitudinally on the conical trailing section for generating spin dampening torque to cause gyroscopic instability and thereby create high aerodynamic drag upon said projectile when fired from a weapon.

GOVERNMENTAL INTEREST

The invention described herein may be manufactured, used and licensed byor for the Government for Governmental purposes without payment to us ofany royalties.

BACKGROUND OF THE INVENTION

The present invention relates to ammunition for low caliber weapons. Inparticular, the invention relates to ammunition for low caliber weaponscontaining an improved ball for training purposes. More particularly,the present invention relates to a projectile or ball for trainingammunition which must have a limited range.

As used herein, the term "ball" is defined as a bullet for general use,as distinguished from bullets for special uses such as armor-piercing,incendiary, or high explosives. In particular, the term "ball" relatesto any low caliber projectile regardless of its shape.

Many military training facilities do not have sufficient real estate toaccommodate the range of standard ammunition, yet they are required toprovide a realistic training environment. The training ammunition mustballistically match the standard ammunition for the weapon to themaximum range of interest. Additionally, it should be similar inappearance to the standard ammunition in order to afford realistictraining.

In order to find an appropriate ball for a limited range trainingammunition, both plastic balls and steel probe nose rounds have beenstudied and their performance was determined to not be as required. Themaximum range of the plastic ball at 40° quadrant elevation was found tobe about 2936 meters, and the steel probe nose round was found to have arange of about 3957 meters. In contrast, the required maximum range forlimited range training ammunition is 2500 meters. Thus, both the plasticball and the steel probe nose rounds exceeded the safety limit forrange. In addition, in the testing of .50 caliber plastic ball rounds,the mass of the rounds was found to be insufficient to generate enoughrecoil for recycling the M2 Machine Gun at a satisfactory level.Moreover, neither the plastic ball rounds nor the steel probe noserounds looked similar to the Caliber .50, M33 ball. This has an effectupon the reality of the training environment, since the Caliber .50, M33ball is the standard service round for the M2 Machine Gun.

Accordingly, it is an object of the present invention to provide smallcaliber training ammunition containing a projectile having a limitedrange.

It is a further object of the present invention to provide trainingammunition containing a projectile having limited range, which issimilar in appearance to the standard ammunition for the weapon in use.

It is a further object of the present invention to provide suchammunition, wherein the expense of the projectile is not excessive incost, in comparison to the projectile of the standard ammunition for theweapon in use.

These and other objects of the invention, as well as the advantagesthereof, will become clear from the disclosure which follows.

SUMMARY OF THE INVENTION

The present invention provides a training projectile which may be shapedexternally similar to the Caliber .50, M33 ball, which is the standardammunition to be fired from the M2 Machine Gun, or shaped similar to anyother suitable ammunition.

Accordingly, the present invention comprehends a projectile or ball,which is suitable for use in limited range training ammunition, whichhas a projectile body having a tapered forward section, a cylindricalcenter section, and a tapered trailing section. A plurality of fins ismounted longitudinally on the tapered trailing section of the projectilebody. The fins generate a spin dampening torque to cause gyroscopicinstability and thereby create high aerodynamic drag upon the projectilewhen fired from the weapon of use.

In a particular embodiment of the present invention, the projectiletapered forward section has an ogival shape and the projectile bodytapered trailing section has the configuration of a truncated cone. Theprojectile is further characterized by four straight fins mountedradially on the tapered trailing section of the projectile body at 90°intervals about the projectile body longitudinal axis.

A clearer understanding of the present invention will be obtained fromthe disclosure which follows when read in light of the accompanyingdrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings illustrate various embodiments of theinvention.

FIG. 1 is a front elevational view of the small caliber projectile ofthe present invention.

FIG. 2 is a left side elevational view of the projectile of FIG. 1,shown enlarged for purposes of clarity.

FIG. 3 is a graph of drag force coefficient versus projectile velocityin Mach number.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring now to FIGS. 1 and 2, there is shown a projectile 10 forlimited range training ammunition. Projectile 10 has a projectile bodycontaining a tapered forward or leading section 11, a cylindrical centersection 12, and a tapered rearward or trailing section 13. Thecylindrical center section 12 contains a circumferential recess 14 forclamping a copper jacket or cartridge casing to the projectile body. Asillustrated, the circumferential recess 14 preferably has a knurledsurface. The tapered forward or leading section 11 may have a conicalconfiguration, but it preferably has an ogival configuration, asillustrated, since this is the shape of the standard Caliber .50, M33ball. A spherical nose 15 is located on the leading end of the ogivalforward section 11. This rounded or spherical nose is generally lessthan a full hemisphere. It may be a portion of a hemisphere of acircular sphere or it may be a portion of an elliptical sphere.Preferably, the nose curvature for the spherical nose 15 is designed tomatch the aerodynamic axial force of the standard service projectile.The tapered rearward or trailing section 13 preferably is in the form ofa truncated cone.

A circular trailing end face 16 is on the rear end of conical section13. A plurality of straight fins 17 is mounted on the trailing conicalend section 13 and the trailing end face 16. As shown in FIGS. 1 and 2,it is preferred that the plurality of fins be four fins mounted radiallyon the tapered trailing section at 90° intervals about the longitudinalaxis of the projectile body. However, it is within the scope of theinvention to have fewer or more straight fins as may be desired.

The presence of the fins on the projectile body has two influences inits flight. The first influence is to decrease the spin of theprojectile in order to induce gyroscopic instability. The secondinfluence is to produce high drag at high angles of attack or highangles of incidence with respect to the air stream. When the projectileis nose-on into the air stream, the fins have little effect on drag, butas the spin decreases, the projectile begins to yaw in a conicaloscillation so that the fins begin to take more and more effect, andgreater and greater aerodynamic drag is created until the projectiletumbles to the earth.

This is in direct contrast to the effect of the prior art fins on otherdevices such as bombs, rockets, torpedoes, and mortar projectiles. Thefins on such devices are used to weathervane the device in its flight.That is to say, the fins point into the wind or air stream flowing overthe device in flight (water stream in the case of a torpedo), so thatwhen the device begins to pivot, the fins act as a weather vane in thewind to bring the device back into alignment with the flight path andkeep it stable. Thus, the prior art fins act to keep the device stablein flight and thereby maximize accuracy and range, whereas the fins ofthe present invention act to destabilize the device in flight andminimize range.

Projectiles of the present invention have been tested on the smallcaliber range at Fort Dix, N.J. on the M2 Machine Gun. The results haveshown that the inventive projectile matched the ball of the standardservice round to velocities having a Mach number of from about 1.48 toabout 1.58. The projectiles thereafter became unstable at lowervelocities. The distance that corresponds to this range of Mach numbersis from about 975 meters to about 1100 meters, and the predicted maximumrange for the inventive projectile was found to be about 1600 meters.This means that all projectiles become unstable and begin to tumble andfall in the range of from about 975 to 1100 meters, and that no matterwhat elevation the weapon is fired at, all projectiles will be on theground before reaching 1600 meters. Moreover, the test showed that theinventive projectile recycles the M2 Machine Gun without any problems.

FIG. 3 provides an indication of the test results from the Fort Dixsmall caliber range. It shows the rapid increase in aerodynamic drag atthe aforementioned Mach number, thereby limiting the range of theprojectile. It will be seen that as the velocity is reduced, the dragcoefficient increases at a low rate, but upon reaching a Mach number offrom about 1.48 to about 1.58, the drag force coefficient increasesgreatly at a rapid rate. This is the point at which the projectilebecomes unstable and begins to tumble and fall to the earth. In thetitle of FIG. 3, the term "CAL.50 LRTA" means Caliber .50 Limited RangeTraining Ammunition.

The Caliber .50 projectiles which were tested at Fort Dix had theappearance of the projectile shown in FIG. 1, with an ogival nose andfour straight fins radially mounted about the longitudinal axis at 90°intervals. The overall length of the projectiles was about 2.821 inch.The surface of the ogival forward section 11 had a curvature having aradius of about 4.0 inches and the radius of the spherical nose 15 wasabout 0.039 inch. The length of the ogival forward section 11 was about1.365 inches and the length of the cylindrical section 12 was about0.559 inch. The tapered section 13 had a length of about 0.386 inch andit had a slope of 7°±30'. The knurled recess 14 had a width of about0.080 inch and its forward edge was about 1.500 inches from the nose ofthe projectile. The fins extended back about 0.511 inch from thetrailing face 16, and they had a thickness of about 0.031 inch. Theprojectiles had an outer diameter of about 0.511 inch through thecylindrical center section 12, and the outer diameter of the fins wasabout 0.464 inch. Thus, the fins had an outermost radial dimension whichwas less than the outermost radial dimension of the projectile body, andthe forward end of the fins terminated on the sloped surface of thetapered trailing section 13 intermediate the trailing end face 16 andthe junction line between the tapered trailing section 13 and thecylindrical center section 12, as shown in FIGS. 1 and 2. Those skilledin the art will recognize that when the projectile is contained within acartridge casing or jacket, the fins must have an outermost radialdimension which is not greater than the outermost radial dimension ofthe projectile or the inner radial dimension of the jacket, so that thefinned projectile can fit within the jacket.

Although the tests of the inventive projectile were made with Caliber.50 balls of the present invention being fired from the M2 Machine Gun,projectiles of the present invention also will be useful in limitedrange training ammunition for other small caliber weapons. The inventiveballs will preferably use a copper jacket externally and a soft steelcore. However, the invention is not limited to small caliber ammunition.It also has utility for larger projectiles, such as those projected bymortar or artillery, where a limited range is required.

It is important to note that the length of the fins must be sufficientto impart a spin dampening torque on the otherwise spin stabilizedprojectile during flight in order to cause gyroscopic instability andthereby create high aerodynamic drag. As noted hereinabove, the fins onthe Caliber .50 projectile of FIG. 1 extended back about 0.511 inch fromthe trailing face 16. This dimension will differ for different sizeprojectiles, and the length needed for a given size projectile can onlybe determined by empirical testing.

The foregoing disclosure and drawings are merely illustrative of theprinciples of this invention and are not to be interpreted in a limitingsense. We wish it to be understood that we do not desire to be limitedto the exact details of construction shown and described because obviousmodifications will occur to a person skilled in the art.

We claim:
 1. In combination, a projectile for use on a limited rangetraining ammunition consisting essentially of:a. a projectile bodyhaving a tapered ogival forward section, a cylindrical center section,and a tapered conical trailing section,1. said tapered ogival forwardsection having a rounded leading nose,
 2. said cylindrical centersection having a circumferential recess for the clamping of a cartridgecase to said projectile bodya. said recess having a knurled surface, 3.said conical tapered trailing section having the configuration of atruncated cone,a. said tapered conical trailing section terminating in acircular trailing end face, b. a plurality of straight fins mountedlongitudinally on said tapered conical trailing section for generatingspin dampering torque to cause gyroscopic instability thereby creatinghigh aerodynamic drag upon said projectile when fired from a weapon,1.said fins mounted on the surface of said truncated cone,
 2. said finsmounted on said tapered trailing section at 90° intervals about saidprojectile body,
 3. said fins extending rearwardly from said taperedtrailing section, and
 4. said fins terminating beyond said circulartrailing end face,
 5. said fins having an outermost radial dimension notgreater than the outermost dimension of said projectile body.